System, Apparatus and Method For Producing A Well

ABSTRACT

A system is provided that is capable of providing heat across a produced interval during oil and gas production to minimize or reduce undesirable formation of gas hydrates in the wellbore. In one embodiment, the configuration provides a means to recycle heat generated by an electrical submersible pump. Heat from the pump may be applied downhole. One configuration is capable of providing for downhole separation of gas from produced fluids to reduce or eliminate gas transit through the pump. A heating element also may apply heat to produced fluids. In one embodiment, a system may provide for the safe containment and control of gas within the wellbore by the utilization of a safety valve.

CROSS REFERENCE TO RELATED INVENTIONS

This application claims priority to and relates to an earlier filed U.S. provisional application Ser. No. 61/524,596 which was filed in the United States Patent and Trademark Office on Aug. 17, 2011.

FIELD OF THE INVENTION

The invention is directed to a system, apparatus and method for producing fluids and gas from a wellbore.

BACKGROUND OF THE INVENTION

A problem in the production of oil and gas from subsea wellbores is the undesirable formation of gas hydrates. A gas hydrate is a crystalline solid consisting of molecules of gas, usually methane, surrounded by a “cage” of water molecules. Gas hydrates have the visual appearance of ice. Methane hydrate is stable in ocean floor sediments at water depths of greater than about 300 meters. Certain temperature and pressure conditions encourage the formation of gas hydrates.

Gas hydrates pose a problem for the oil and gas industry as more deepwater gas enters the supply stream. Gas hydrates may form inside pipelines or in wellbores, slowing or completely blocking flow of hydrocarbons. Hydrate formation is a serious problem for producers moving gas from offshore wells to onshore processing facilities. Clearing plugged lines is expensive and time-consuming, and may take as long as twenty days. It has been estimated that controlling and preventing gas hydrate formation costs the industry hundreds of millions of dollars annually. It is very important to make changes or adjustments in wellbores to reduce the likelihood of gas hydrate formation.

In the production of oil and gas, it is sometimes necessary to employ downhole electrical submersible pumps to assist in moving oil from the formation to the surface in the wellbore. Submersible pumps are used in such operations to provide a relatively efficient form of “artificial lift”. By decreasing the pressure at the bottom of the well, more oil can be produced from the well when compared with natural production. Such pumps typically are electrically powered and may be referred to as Electrical Submersible Pumps (“ESP”).

ESP systems may be subject to undesirable cavitation if excess gas is present in the flow stream being pumped. Shock waves caused by cavitation in pumps may damage moving parts within the pump. It is desirable to avoid entrained gas in production fluids that are to be pumped by a downhole ESP to avoid damage to pumps.

SUMMARY OF THE INVENTION

A system, apparatus and method is provided for producing oil and gas from a wellbore within a subterranean formation. The system comprises a wellbore lined with a casing, the wellbore having an upper end and a lower end, the lower end of the wellbore being adjacent the subterranean formation. The casing is tubular in shape with an interior cavity. Casing is installed in sections when the well is constructed, with each successive section of casing installed in the drilled well being slightly smaller in diameter than the prior section of casing. Production tubing is positioned within the interior cavity of the casing. A pump may be connected to the production tubing, the pump being adapted for lifting hydrocarbons within the production tubing.

An isolation sleeve may be positioned circumferentially outside of the production tubing and within the interior cavity of the casing. An inner space may be located between the isolation sleeve and the production tubing. An outer space also may be positioned between the isolation sleeve and the casing. The isolation sleeve may be configured to facilitate the upward movement, within the outer space, of production fluids and gas towards the upper end of the wellbore. Gas is separated from the production fluids, and the isolation sleeve may be configured to facilitate the downward movement, within the inner space, of production fluids toward the lower end of the wellbore.

A pump may be adapted for transmission of heat to the production fluids in the inner space, thereby elevating the temperature of the production fluids. The system may be configured for transferring heat carried by the production fluids to the lower end of the wellbore to reduce the formation of gas hydrates in the wellbore. In general, adding heat to the lower end of the wellbore assists in inhibiting undesirable gas hydrate formation.

In one specific aspect of the invention the system also comprises a heating element positioned to contact production fluids in the inner space. Further, a ported bushing sub may be employed to receive production fluids and gas from the outer space and facilitate the movement of the production fluids to the inner space. The ported bushing sub may be positioned adjacent a gas collection space. Production fluids and gas from the inner space may proceed through the ported bushing sub for separation, so that gas is accumulated in the gas collection space while production fluids are provided to the inner space for transport further down into the wellbore.

In yet another embodiment of the invention, an annular seal locator sub may be positioned above the gas collection space. The annular seal locator sub may be configured for releasing gas from the gas collection space towards the upper end of the wellbore. A safety valve may be positioned upon the annular seal locator sub for controlling gas release from the gas collection space. The ported bushing sub may be adapted for sealed engagement with a polished bore receptacle (a “PBR”).

In one embodiment of the invention, at least one heating element is provided upon or adjacent the production tubing. The method may include the additional step of transferring heat from the heating element to the production fluids and applying such heat towards the lower end of the wellbore. Further, production fluids may be pumped through the production tubing towards the upper end of the wellbore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross sectional view of one embodiment of the system of the invention.

DETAILED DESCRIPTION OF THE INVENTION

A system, apparatus and method is provided that is capable of providing heat across a produced interval during oil and gas production that may serve to minimize or reduce undesirable formation of gas hydrates in the wellbore. In one embodiment the configuration provides a means to recycle and conserve heat generated by an electrical submersible pump (“ESP”). Also, it may be possible in some applications to provide additional heat downhole by the use of one or more heating elements to apply heat to produced fluids that are circulated downhole, thereby minimizing the undesirable formation of gas hydrates within or adjacent to the wellbore interface. An isolation sleeve may be employed that extends across the completion interval and is sealed near the bottom in a seal receptacle, causing the flow stream from the wellbore to flow up the outside of the isolation sleeve. The fluids and gas may be separated, as further described herein. Also, such heat could assist in producing heavy oil in some applications, by making the heavy oil less viscous and more capable of flow.

In one embodiment, the configuration is capable of providing for downhole separation of the gas to reduce or eliminate gas from being produced through an ESP. Producing gas through an ESP is undesirable, as it may damage the pump by way of cavitation or “gas lock”. The system in one embodiment may provide for the safe containment and selective release of gas within the wellbore by the utilization of an annular safety valve.

Turning to FIG. 1, an example of the invention is shown. A subterranean formation 28 contains a wellbore upper end 20 and wellbore lower end 26 (seen at the upper and lower portions of FIG. 1). A casing 22 extends into the wellbore and is cemented in place with cement 24. Production tubing 32 is shown in the central portion of FIG. 1, extending through the annular seal locator sub 34 and the ported bushing sub 56. The annular seal locator sub 34 mates with polished bore receptacle 36 in a gas tight seal. A cement plug 38 seals against the inside surface of the casing 22 circumferentially around the periphery of casing 22. Further, inner casing 23, is cemented in place by cement 25. The inner casing 23 mates with polished bore receptacle 36 to form a seal.

An optional heating element 40 may be provided as shown in association with the production tubing 32 and in position to contact production fluids to transfer heat to production fluids. Electrical submersible pump (ESP) 42 also is provided in association with production tubing 32 and is provided to provide pumping pressure to assist in moving production fluids upwards within production tubing 32. An isolation sleeve 44 is provided, and it is associated with the ported bushing sub 56. The isolation sleeve 44 separates and defined an outer space 46 from inner space 48. The outer space receives commingled production fluid comprising gas and liquids, while the inner space contains primarily only liquid production fluids. The separation of the gas from the production fluids will occur in the gas collection space 58, as further discussed herein. Gas may be released through gas release line 60 upon opening of valve 49.

The flow of production fluids begins in subterranean formation 28 and proceeds through perforations 57 in lower casing joint 55. The pathway of production fluids proceeds along arrow 54 a within inner space 48 towards the wellbore upper end 20. At gas collection space 58, the gas portion of the production fluids is collected, while the liquid portion of production fluids proceeds through the ports (not shown) of the ported bushing sub 56 downwards towards the wellbore lower end 26 along arrow 54 b into inner space 48. At point 50, the liquid portion of the production fluids within inner space 48 is in position to collect heat generated by the optional heating element 40 and proceed further downwards within the inner space 48 to point 52. At point 52, the liquid portion of the production fluids receive heat from the ESP and continue to travel downwards towards arrow 54 c and then to arrow 54 d. The heated liquid portion of the production fluids transmit heat to the wellbore lower end 26 to assist in preventing the formation of gas hydrates in the wellbore lower end 26. Fluids travel along the path of arrow 54 e, where they change direction and then proceed upwards along arrow 54 f into the production tubing 32. Production tubing 32 contains release valve 47. Fluids are produced from the wellbore upper end 20 through production tubing 32.

In the practice of the invention, many different equipment sizes may be employed. However, one embodiment of the invention, as shown, employs a polished bore receptacle 36 having a 15 inch internal diameter in the bottom of an 18⅝ inch casing 33. Further, the production tubing 32 may be 4½ inch in diameter in the embodiment shown in FIG. 1.

The ported bushing sub 56 may be a triple bushing sub, also known as a triple connection bushing. Such a bushing comprises three connections—a washpipe connection and two drillpipe connections. The ported bushing sub 56 may be run in connection with a backoff or packer retrieving assembly. The triple connection bushing sub may be employed for a bottom hole assembly requiring an inside and outside assembly. The outside diameter is built per specifications of the washpipe connection and the internal diameter is determined by the specifications of the smaller drillpipe connection.

One example of a suitable isolation sleeve 44 is of a size 11¾ inch×8⅝ inch. A gravel pack with perforations 57 is commonly used in such an application. A sump packer 62 is shown near the lower portion of FIG. 1.

The invention is shown by example in the illustrated embodiments. However, it is recognized that other embodiments of the invention having a different configuration but achieving the same or similar result are within the scope and spirit of the claimed invention. 

1. A system for producing oil and gas from a wellbore penetrating a subterranean formation, the system comprising: (a) a wellbore lined with a casing, the wellbore having an upper end and a lower end, the lower end of the wellbore being adjacent the subterranean formation, further wherein the casing is tubular in shape with an interior cavity; (b) production tubing positioned within the interior cavity of the casing; (c) a pump connected to the production tubing, the pump being adapted for lifting hydrocarbons within the production tubing; (d) an isolation sleeve positioned circumferentially outside of the production tubing and within the interior cavity of the casing, (e) an inner space between the isolation sleeve and the production tubing; (f) an outer space between the isolation sleeve and the casing; (g) the isolation sleeve being configured to facilitate the upward movement, within the outer space, of production fluids and gas towards the upper end of the wellbore; (h) the isolation sleeve being configured to facilitate the downward movement, within the inner space, of production fluids toward the lower end of the wellbore; (i) the pump being adapted for transmission of heat to the production fluids in the inner space, thereby elevating the temperature of the production fluids; (j) the system being configured for transferring heat carried by the production fluids to the lower end of the wellbore to reduce the formation of gas hydrates in the wellbore.
 2. The system of claim 1, the system further comprising a heating element positioned to contact production fluids in the inner space.
 3. The system of claim 1 further comprising a ported bushing sub, wherein the ported sub is configured to receive production fluids and gas from the outer space and facilitate the movement of the production fluids to the inner space.
 4. The system of claim 3 wherein the ported bushing sub is positioned adjacent a gas collection space, wherein production fluids and gas from the inner space may proceed through the ported bushing sub for separation such that gas is accumulated in the gas collection space while production fluids are provided to the inner space for transport downhole.
 5. The system of claim 4 wherein an annular seal locator sub is positioned above the gas collection space, the annular seal locator sub being configured for releasing gas from the gas collection space towards the upper end of the wellbore.
 6. The system of claim 5 wherein a safety valve is positioned upon the annular seal locator sub for controlling gas release from the gas collection space.
 7. The system of claim 3 wherein the ported bushing sub is adapted for sealed engagement with a polished bore receptacle.
 8. A method of producing oil and gas from a wellbore, the wellbore having a casing penetrating a subterranean formation, the wellbore having an upper end and a lower end, the method comprising: (a) providing production tubing within an interior cavity of a casing, the production tubing being connected to a pump, the pump being adapted for lifting hydrocarbons within the production tubing; (b) providing an isolation sleeve positioned circumferentially outside of the production tubing and within the interior cavity the casing, there being an inner space between the isolation sleeve and the production tubing, further providing an outer space between the isolation sleeve and the casing; (c) moving production fluids and gas within the outer space towards the upper end of the wellbore; (d) separating the production fluids from the gas; (e) moving production fluids downward within the inner space adjacent the pump; (f) transferring heat from the pump to the production fluids; (g) elevating the temperature of the production fluids; (h) transferring heat carried by the production fluids towards the lower end of the wellbore; and (i) reducing the formation of gas hydrates in the wellbore.
 9. The method of claim 8 wherein at least one heating element is provided upon or adjacent the production tubing, the method comprising the additional step of transferring heat from the heating element to the production fluids and transferring such heat towards the lower end of the wellbore.
 10. The method of claim 8 further comprising the step of: (j) transporting the production fluids through the production tubing towards the upper end of the wellbore.
 11. A system for isolating gas in a wellbore, the wellbore having a casing with an interior cavity formed by an interior surface, the wellbore having an upper end and a lower end, the system comprising: (a) a polished bore receptacle forming a seal with the interior surface of the casing; and (b) an annular seal locator sub mated with the polished bore receptacle, the annular seal locator sub being configured to form a gas-tight collection space below the annular seal locator sub to collect gas within the casing of the wellbore, the annular seal locator sub further comprising at least one gas-tight penetration adapted for a safety valve, further wherein the system is configured to control the release of gas from the wellbore.
 12. The system of claim 11 further comprising production tubing positioned within the casing and extend through the annular seal locator sub.
 13. The system of claim 12 further comprising a pump connected to the production tubing, the pump being positioned downhole from the annular seal locator sub, the pump further being adapted for lifting hydrocarbons within the production tubing.
 14. The system of claim 13 further comprising an isolation sleeve positioned circumferentially outside of the production tubing and within the casing.
 15. The system of claim 14 further comprising: (a) an inner space between the isolation sleeve and the production tubing and (b) an outer space between the isolation sleeve and the casing.
 16. The system of claim 15 wherein the isolation sleeve is configured to facilitate the upward movement, within the outer space, of production fluids and gas towards the upper end of the wellbore.
 17. The system of claim 16 wherein the isolation sleeve is configured to facilitate the downward movement, within the inner space, of production fluids toward the lower end of the wellbore.
 18. The system of claim 17 wherein the pump is adapted for transmission of heat to the production fluids in the inner space, thereby elevating the temperature of the production fluids.
 19. The system of claim 18 wherein heat is carried by the production fluids to the lower end of the wellbore to minimize the formation of gas hydrates in the wellbore.
 20. The system of claim 19 further comprising a heating element positioned as to contact production fluids in the inner space. 